Drilling vessel

The drilling vessel

DRILLING VESSEL (EN: drilling vessel; DE: Bohrschiff; FR: navire de forage; ES: barco perforador; RU: буровое судно) is the floating built structure for the marine drilling of the boreholes, which is equipped with the central cutout within the hull, above which there is installed the drilling derrick, and with the system for the retention of the vessel above the mouth of the borehole.

For the first time, the drilling with the usage of the drilling vessel has been started within the Atlantic ocean during the 1968 (from the "Glomar Challenger" American vessel). The modern drilling vessels (see the Figure) are, as a rule, self-propelled, with the unlimited region for the navigation. The water displacement of the drilling vessel is 6-30 thousand tonnes, the deadweight is 3-8 thousand tonnes, the power of the energetic installation, which is supplying the drilling works, positioning, and movement of the vessel, is up to 16 megawatts, the speed of the movement is up to 15 knots, the autonomy according to the reserves is 3 months. There are used on the drilling vessel the stabilizers against the roll, allowing to conduct the drilling of the boreholes during the roughness of the sea of 5-6 points of magnitude; during the great roughness of the sea, the drilling is interrupted, and the vessel is laid up into the storm, with the distancing from the borehole (the distance is up to 6-8% of the depth of the sea), or the drilling pipe string is disconnected from the mouth of the borehole. For the retention of the drilling vessel in the required point of the drilling within the limits, which are acceptable for the rigidity of the drilling pipe string, they use 2 systems for the positioning: the static system (with the usage of the anchoring for the vessel), and the dynamic stabilization (with the help of the propellers, and of the auxiliary thruster steering devices).

The anchoring system is used for the drilling vessel in case of the depth of the sea of up to 300 metres; it includes the ropes and chains, the special anchors with the mass of 9-13.5 tonnes (8-12 anchors), the anchoring winches with the tension of 2 meganewtons each, which are equipped with the monitoring-measuring apparatuses. The placement of the anchors, and their retrieval, are performed by the auxiliary vessels. For the increase of the maneuverability, and for the decrease of the time of work during the departure from the point of the drilling, they use the so-named anchoring systems for the circular orientation of the vessel (the turret, which is specially built into the centre of the hull of the vessel, with the platform, onto which there is mounted all the anchoring device, including the winches). The retention of the drilling vessel at the position, with the help of the system for the dynamic stabilization, is used for the vessels of any class, in case of the depth of the sea of more than 200 metres, and is performed automatically (or manually) with the help of the measuring, informative-commanding, and propulsion-steering complexes.

There belong to the structure of the measuring complex the instruments of the acoustic system, which are used for the stabilization of the vessel during the mode for the drilling, during the installation of the vessel above the borehole, for the determination of the position of the water-separating pipe string relatively to the mouth of the borehole. The work of the acoustic system is based on the registration of the impulses, which are sent from the bottom beacons, which are placed near the mouth of the borehole, and on the receiving of these impulses by the hydrophones under the bottom of the vessel. As the double-redundant system, they use the inclinometer. There belong to the structure of the informative-commanding complex the 2 computers, which are receiving simultaneously the information about the position of the vessel, and about the condition of the environment; during this process, one of these computers works in the command mode, and is controlling the motors, while the second (reserve) computer works automatically (in case of the failure of the first computer). The propulsion-steering complex includes the main movers of the vessel, the auxiliary thruster steering devices, and the system for the control of this equipment. The forces for the longitudinal fixation on the vessel are created by the propellers with the controllable pitch, while the forces for the transversal fixation are created by the special propellers with the controllable pitch, which are installed within the transverse tunnels within the hull of the vessel. The changing of the magnitude and of the directions for the fixation is performed using the adjustment of the controllable pitch for the propellers, according to the command by the computer, or manually from the control board for the propulsion system.

The drilling vessel is equipped also with the control board, which is purposed for the monitoring of the position of the vessel, and of the water-separating pipe string, during the mode for the automatic stabilization, and with the remote manual control during the installation of the vessel onto the position. The variety of the drilling vessel is the so-named hose-cable vessels, which are purposed mostly for the engineering-geological drilling at the depth of 200 metres, in case of the depth of the sea of up to 600 metres. They are equipped with the system for the dynamic stabilization, and with the flexible hose-cable, thanks to which the requirements for the distancing of the vessel relatively to the mouth of the borehole are less strict, than in case of the usage of the drilling pipes.